Method of preparing metal sealing surfaces



April 29, 1969 R. cs. MILLHISER 7 3,440,703

METHOD OF PREPARING METAL SEALING SURFACES Original Filed Aug. 31, 1964F/GJ INVENTOR Ease/2T 6. M11. 111/652,

United States Patent M 3,440,703 METHOD OF PREPARING METAL SEALINGSURFACES Robert G. Millhiser, Detroit, Mich., assignor to AjemLaboratories, Inc., Livonia, Mich. Original application Aug. 31, 1964,Ser. No. 393,045, now Patent No. 3,314,684, dated Apr. 18, 1967. Dividedand this application Dec. 21, 1966, Ser. No. 604,112 Int. Cl. B23p 00,-B24b 1/00; B24c 1/00 US. Cl. 29156.4 7 Claims This is a divisional ofapplication Ser. No. 393,045, filed Aug. 31, 1964, now Patent No.3,314,684.

This invention relates to methods and articles resulting therefrom forcreating greatly superior sealing surfaces, and more particularly formaking a revolutionary kind of stationary gasket surface or slidingmetal-to-metal sealing surface.

In prior applications for myself and my co-workers we have disclosedprocesses and apparatus for reforming and improving surfaces of variousarticles by impacting them with abrasive or shot-peening particles(which will be referred to herein as grit) accelerated to surfacereforming velocities. Such processes and apparatus for performing themhave been disclosed in a series of applications, e.g., Ser. No. 9,910,filed Feb. 19, 1960, Patent No. 3,150,- 467, dated Sept. 29, 1964; Ser.No. 112,454, filed May 24, 1961, Patent 3,153,882 issued Oct. 27, 1964;Ser. No. 122,521, filed July 7, 1961, Patent No. 3,146,550, dated Sept.1, 1964; Ser. No. 105,978, filed Apr. 27, 1961, Patent No. 3,160,989,issued Dec. 15, 1964; Ser. No. 176,084, filed Feb. 27, 1962, nowabandoned.

We shall use the term surface reforming herein to include the varioussurface treatments by which a new surface is formed on a part, or one ofits characteristics is changed in some respect from those of the partbefore such treatment. In other words, surface reforming which includesthe actual removal of minute portions of surface material or an actualmolecular alteration or crystalline rearrangement of such surfacematerial. This surface reforming in the present invention includesbombardment of the surface with hard particles, i.e., grit includingespecially steel shot or short pieces of cut wire, sand, aluminum oxide,silicon carbide or the like, all of which are known to the art ingeneral as grit for blasting treatment.

In finishing metal surfaces and the like for gasketing or other sealingpurposes, it has been the general practice to prepare the surfaces byvery fine cuts with machine tools, grind them with fine abrasives, e.g.,grinding wheels or laps, or to lap or hone them with grinding compounds,for example, which consist of abrasives in liquid lubricant carriers.These former practices result in machine or grinding lines in the formof small to medium size grooves. These extended linear imperfections inthe sealing surface generally occur multiply, often in a cross-hatchpattern, resulting in a series of escape paths in the form of minutegrooves along which the compressed fluid can flow through a sealingjoint. Often the gases escaping along these paths are quite corrosiveand can cause progressive deterioration of the sealing joint withultimate, even if not immediate, total failure of the seal. In theautomotive industry, in order to overcome gasket failures in engineheads it has been found necessary to prepare the sealing surface with aseries of increasingly fine cuts, first with a tool and then with agrinding wheel, necessitating a tedious and expensive procedure. Withthis procedure, the surface of the engine head had to be groundextremely smooth, e.g., with an aluminum engine head to a profiltometerreading of between 10 to microinches. In spite of such carefulpreparation the industry still experienced gasket failures.

According to the present invention, I have found the 3,440,703 PatentedApr. 29, 1969 surprising result that it is not the microinch reading ofroughness (which had heretofore been the criterion of sealing surfaceexcellence) which was significant, but rather what I shall call thesurface texture which is actally significant. I have found that byimpinging grit under certain controlled conditions, preferably impelledby a liquid medium, against the proposed sealing surface, I can achievesuperior seals even though the sealing surfaces have a microinch readingof two to four times what had formerly been thought possible, and evenmore. I believe that my success results from the obliteration of theirregular machine marks left in the original roughing out of the sealingsurface. This obliteration by grit impingement apparently breaks upthese linear imperfections, thereby blocking off potential paths ofescape, by forming a substantially uniform surface having a multiplicityof contiguous shallow pits. These pits can serve a dual purposedepending upon the specific use to which the prepared sealing is to beput. For example, in a static seal the ridges formed between these pitsbite into the opposing surface thereby giving a series of thousands ofsuccessive minute barriers across the sealing surface, thereby multiplyblocking off any potential escape path. In the case where a plasticsealant or the like is employed, these pits present an irregularroughness which enhances the grip of the sealant onto the surface andenable it to better resist external pressures. In the case of slidingparts, these pits can similarly act as minute reservoirs of lubricant tomaintain lubrication of the surface and to permit the ridges to seal inthe same manner as indicated above.

Besides forming a multiplicity of pits by gouging or displacement, thisgrit impingement apparently also compacts the surface to close over andfill any machine grooves or other micro-fissures.

The surprising improvement in the operation of such devices whichresults from such treatment of these surfaces is not at present fullyunderstood and therefore I cannot be bound by any theory. However, itappears from the evidence considered, that this is probably due to theforegoing explanations. The use of the aforementioned methods developedby myself and my co-workers on malleable surfaces, such as metal andcertain plastics, to

give a reformed surface having a multiplicity of contiguous shallowpits, have proven in actual tests in the field to give greatly improvedsealing fitted surfaces, especially for holding fluid pressures as incylinder heads, pipe flanges, and valve housings and/or sliding surfacesas in valves, pistons, and cylinders, etc.

In this specification and the accompanying drawings We have shown anddescribed a preferred embodiment of our invention and have suggestedvarious alternatives and modifications thereof; but it is to beunderstood that these are not intended to be exhaustive and that manyother changes and modifications can be made within the scope of theinvention. These suggestions herein are selected and included forpurposes of illustration in order that others skilled in the art willmore fully understand the invention and the principles thereof and willthus be enabled to modify it and embody it in a variety of forms, eachas may be best suited to the conditions of a particular use.

In the accompanying drawings:

FIGURE 1 shows a side elevation and section of a piston and cylindercombination having a gasketed head, the walls of said cylinder and theopposing faces of the gasket portions of said head representing sealingsurfaces according to the present invention;

FIGURE 2 illustrates a greatly enlarged schematically representationalcross section of the gasket surface of the head shown in FIGURE 1, asthough taken along line 2-2; and

FIGURE 3 is a similar schematically representational enlarged sideelevation of a portion of the cylinder wall.

The generalized piston and the cylinder block 12 shown in FIGURE 1illustrate an example of a possible use for the sealing surfaces of thepresent invention. FIG- URE 1 could represent uses of this invention onsuch widely divergent apparatus as a portion of an aluminum automotiveengine head or part of a precision pump.

Looking at the apparatus illustrated in FIGURE 1 as an internalcombustion engine, one can see two different applications of the presentinvention, namely (1) as a static sealing surface on the gasket portion14 of the engine head 16, and (2) as a sliding sealing surface on thecylinder wall 18 of the cylinder block 12.

The type of surface reforming required for the preparation of thesedesired sealing surfaces varies greatly according to the use to which itwill be put. If an aluminum engine head gasket surface is to beprepared, then it has been found that a liquid impelled abrasive blastgenerated at a pressure of 115 p.s.i. and utilizing a 50-50 mixture ofSAE No. and SAE No. 40 grit and directed in a contained stream at asingle angle of attack gives an extremely reliable seal when used with astandard thin steel sheet gasket 20. This treatment gives a uniformlypitted sealing surface having a microinch roughness reading of 40 to 60,which when seven samples were tested at full throttle, resulted inabsolutely no failures. (See pits 22 schematically indicated in FIGURES2 and 3.) This result was better than would be expected from normallyprepared precision ground engine heads, and was obtained by independentautomotive engineers who prior to testing would not believe that engineheads with such high microinch readings could function at all. However,engine heads are now being prepared for actual production using gritover twice as coarse, namely, SAE No. 16 grit, with an estimatedmicroinch reading on the order of 120 to 150. The kind of grit mostoften employed is short pieces of chopped steel wire.

In contrast, these preferred high velocity liquid impelled abrasiveblasts can employ a very fine grit for preparing a 5 to 10 microinchsealing surface giving greatly superior results when used, for example,in a precision pump having a 0.001 to 0.002 inch gasket, than would beobtained from a similar surface prepared by conventional means.

I have found that by using an abrasive grit other than sand, at gritwhich is denser and less likely to fracture, the surface is cut andcompacted at the same time without requiring separate treatment whichhad originally appeared necessary.

A sealing surface according to the present invention should be pitted soas to be substantially contiguous. The more untreated plateaus remainingbetween pits, the less effective the seal. The pitting should besubstantially uniform in the resulting ridges raised, though notnecessarily in the size of the pits themselves. This is to ensure a goodoverall bite into the opposing seal face without any high ridgespreventing the remainder from seating against the opposing face toestablish the required series of highly multiplied minute barriersacross the sealing joint. The range and degree of roughness requiredwill depend upon the material used and the specific purpose for which itis designed. Thus the higher the pressures encountered, or the smallerthe microinch readings required, the relatively more uniform the pittingshould become.

It has become apparent that the relatively low pressure sand blastingnormally practiced in prior art blasting techniques are not sufficientfor the preparation of most sealing surfaces according to my invention.I find that much greater surface reforming energies are usually required5 than are generated by these earlier techniques.

It is also apparent that scattered blasting, as in an unconfined streamfrom a nozzle or from a slinger wheel or as in random spraying, tend togive inferior seals because of wide variations in pitting that result;probably 1 due to a resulting wide variation of impingement speeds andangles of the individual particles, with the peripheral particles (thelast to impinge on each portion of a surface) tending to groove ratherthan pit the surface.

I claim:

1. A process for manufacturing a seal for a joint between surfaces ofadjoining parts which comprises providing the surfaces to interfit ingross conformity with each other over a substantial area, forming atleast one of the surfaces with substantially continuous cuts, grit 9blasting said cut surface over at least a substantial portion of saidinterfitting area with kinetic energy sufficient to drive said gritparticles against said surface with formation of substantiallycontiguous small pits with continuous relatively sharp barrier ridgestherebetween and pressing said parts together to force said ridgesagainst the interfitting surface to form a stationary seal therewith.

2. The process as claimed in claim 1 wherein said grit blasted surfaceis a metal surface.

3. The method of preparing a metal sealing surface which comprisesforming a metal surface with substantially continuous cuts of apredetermined shape, and thereafter obliterating said surface cuts byhigh energy, uniform grit blasting of said surface at a substantiallyunitary angle to form substantially contiguous, small, 0 independentpits having relatively sharp barrier ridges therebetween and giving saidmetal surface a roughness greater than that conventionally required fora surface prepared solely by substantially continuous cuts.

4. A process as claimed in claim 1 wherein said grit blasting results ina roughness in the range of about ten to two hundred microinches.

5. A process as claimed in claim 1 wherein said grit blasting results ina roughness in the range of about 40 to 150 microinches.

6. A process as claimed in claim 1 wherein one of said surfaces is analuminum alloy.

7. A process as claimed in claim 1 wherein said grit blasted surface isan aluminum alloy and said opposing surface is steel.

References Cited UNITED STATES PATENTS 2,248,530 7/1941 Granger et a151-320 X 55 2,404,816 7/1946 Snyder 277-96 X 2,422,431 6/1947 Melrose51-320 FOREIGN PATENTS 556,257 9/1943 Great Britain.

CHARLIE T. MOON, Primary Examiner.

US. Cl. X.R.

1. A PROCESS FOR MANUFACTURING A SEAL FOR A JOINT BETWEEN SURFACES OFADJOINING PARTS WHICH COMPRISES PROVIDING THE SURFACES TO INTERFIT INGROSS CONFORMITY WITH EACH OTHER OVER A SUBSTANTIAL AREA, FORMING ATLEAST ONE OF THE SURFACE WITH SUBSTANTIALLY CONTINUOUS CUTS, GRITBLASTING SAID CUT SURFACE OVER AT LEAST A SUBSTANTIAL PORTION OF SAIDINTERFITTING AREA WITH KINETIC ENGERY SUFFICIENT TO DRIVE SAID GRITPARTICLES AGAINST SAID SURFACE WITH FORMATION OF SUBSTANTIALLYCONTIGUOUS SMALL PITS WITH CONTINUOUS RELATIVELY SHARP BARRIER RIDGESTHEREBETWEEN AND PRESSING SAID PARTS TOGETHER TO FORCE SAID RIDGESAGAINST THE INTERFITTING SURFACE TO FORM A STATIONARY SEAL THEREWITH.